Hot-runner assembly with internally cooled axially mounted electric actuator

ABSTRACT

A hot-runner injection molding apparatus that facilitates use of electric actuators in a compact design includes a hot-runner manifold defining resin channels for conveying resin to nozzles that serve as conduits for introducing liquid resin into a mold cavity, a valve pin configured for linear movement along a longitudinal axis of the nozzle to control flow of liquid resin through the nozzle, and an electric actuator having a body containing an electric motor, wherein the electric actuator body includes channels for circulating a coolant.

FIELD OF THE DISCLOSURE

This disclosure pertains to a hot-runner injection molding apparatushaving an electric actuator configured for circulating a coolant fluidwithin the body of the actuator to facilitate mounting of the actuatorin close proximity to the hot-runner manifold while preventingoverheating of the electric motor of the actuator, and more particularlyto such apparatus wherein the actuator can be axially assembled on thehot-runner manifold without substantial lateral clearance, allowing aplurality of actuators to be assembled onto the manifold in very closeproximity to each other.

DISCUSSION OF THE PRIOR ART

U.S. Pat. Nos. 9,492,960 and 9,937,648 disclose an apparatus forcontrolling fluid flow to a mold, which includes a manifold, a valve pinhaving a pin axis, a pin connector and a stem, the valve pin beingdrivable into and out of open and closed positions relative to the gate.An electric actuator comprising an electric motor comprised of a motorhousing that houses a drive shaft having a drive gear and a drive axis,a transmission comprised of a gear shaft, the drive gear and thetransmission gear being drivably interconnected and arranged such thatthe drive axis and the gear axis are non-coaxially mounted or disposedrelative to each other, wherein one or the other of the motor housing orthe transmission housing are removably attached to a top clamping ormounting plate that is mounted upstream of the manifold and fixedlyinterconnected to a mold.

U.S. Pat. No. 6,294,122 discloses an injection molding machine includingan apparatus for controlling movement of a pin comprising a plastic meltflow channel having an output end for delivering molten plastic injectedinto the channel under pressure to a mold cavity, wherein the pincomprises an elongated rod having an axis and an end, the pin beingslidably mounted within the channel for movement along its axis withinthe channel, an electrically driven motor drivably interconnected to anactuating mechanism, wherein the actuating mechanism is drivablyinterconnected to the end of the pin, the motor being controllablydrivable to drive the pin through movement along its axis within thechannel.

EP 2679374A1 discloses an apparatus for injection molding of plasticmaterials, which includes a hot runner, at least one injector, includinga nozzle mobile within which is a valve pin driven by a rotary electricmotor and an associated transmission including a screw-and-nut assemblyfor converting the rotation of the shaft of the electric motor into atranslation of the valve pin. At least two from among the valve pin, therotary electric motor and the screw-and-nut assembly are set parallelalongside one another.

BACKGROUND OF THE DISCLOSURE

In a hot-runner injection molding apparatus, the liquid resin (moltenplastic) is maintained in a molten state within channels defined in aheated manifold. The channels convey the molten plastic material from aninjection molding machine to one or more nozzles that convey the moltenplastic to at least one mold cavity via gates defined at an interfacebetween the nozzle and the mold cavity. After the mold cavity is filled,only the mold cavity is cooled to allow removal of a solid molded part.The resin in the manifold channels and nozzles are maintained at atemperature sufficient to keep the plastic in a liquid state, thusreducing cycle time and waste as compared with cold runner injectionmolding apparatuses, wherein the resin conveying channels are definedwithin the mold plates.

Because of the susceptibility of electric actuators to degradation andfailure when exposed to the high temperatures needed at the hot-runnermanifold, hydraulic or pneumatic actuators are typically employed inhot-runner injection molding apparatus to control the flow of moltenresin into the mold cavity (or cavities). In these hot-runner injectionmolding apparatuses employing electric actuators, the electric actuatorsare positioned remotely from the manifold and/or are provided withexternal cooling means (e.g., a cooled plate between the manifold andactuator), adding considerable complexity and expense as compared withthe more conventionally used pneumatic or hydraulic actuators.

Despite these generally recognized disadvantages with electricactuators, they also have advantages, including the ability to moreprecisely control valve pin movement and positioning, which in turn canhave associated advantages pertaining to part quality and productionefficiency.

SUMMARY OF THE INVENTION

This disclosure addresses the need for utilizing electric actuators forcontrolling valve pin position and movement in a hot-runner injectionmolding apparatus, while protecting the actuator from overheating andproviding a more compact apparatus that does not use separate coolingplates or require remote mounting of the actuator. The apparatusincludes a hot-runner manifold having a resin channel for conveying aliquid resin from an injection molding machine toward a mold cavity, anozzle for conveying the liquid resin from an outlet end of the resinchannel to an inlet of a mold cavity, a valve pin configured for linearmovement along a longitudinal axis of the nozzle to control flow of theliquid resin through the nozzle and into the mold cavity, and a directlycooled electric actuator having an electric motor and a linear driveshaft, wherein both the electric motor and the linear drive shaft arecontained within the body of the electric actuator, and wherein thevalve pin is directly or indirectly coupled to the drive shaft such thatlinear movement of the drive shaft produces co-linear movement of thevalve pin.

The directly cooled electric actuator can be mounted in a space betweenthe hot-runner manifold and an upper mounting plate.

In certain aspects of this disclosure, the directly cooled electricactuator is directly and releasably attached to a support having arelatively high resistance to conductive heat transfer (e.g., stainlesssteel or titanium).

In particular embodiments, the directly cooled electric actuator has,within the body of the actuator, a linear drive shaft and a transmissionmechanism that converts rotational movement of the electric motor intotranslational movement of the drive shaft.

In particular aspects of this disclosure, the linear drive shaft has aninternally threaded bore extending along the length of the shaft, andthe body and/or housing of the actuator has openings at opposite ends(e.g., top and bottom) to allow access to the opposite ends of thethreaded bore. This arrangement allows the upper end of the valve pin toextend upwardly into the internally threaded bore for engagement with anexternally threaded valve pin nut. An externally threaded lock nut canbe tightened against the valve pin nut on the side opposite of the valvepin to lock the position of the valve pin relative to the liner driveshaft.

The disclosed arrangement allows the actuator to be assembled onto themanifold along and coincident with the longitudinal axis of the nozzleand valve pin without requiring movement of the actuator laterally(i.e., radially) from the axis, thereby making it possible to designhot-runner injection molding systems (i.e., apparatus) having aplurality of nozzles, valve pins and actuators in closer proximity toeach other than would otherwise be possible.

The arrangement allows an upper end of the valve pin (or a valve pinextension) to be positioned within the drive shaft and therefore withinthe body of the actuator, facilitating a vertically compact design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational cross-section of an apparatus in accordancewith this disclosure.

FIG. 2 is an enlarged view of the actuator and a portion of thehot-runner manifold on which the actuator is supported.

FIG. 3 is a perspective view of an actuator support and mechanism forfixing the valve pin to a linear drive shaft.

FIG. 4 is an enlarged cross-sectional view of an alternate embodiment inwhich the valve pin is indirectly coupled to the actuator drive shaftvia a valve pin extension.

DETAILED DESCRIPTION

Shown in FIG. 1 is a hot-runner assembly 10 for use in delivering liquidresin (typically a molten thermoplastic composition) from an injectionmolding machine (not shown) to a mold cavity 12 defined by mold plates14, 16. The resin flows from the injection molding machine into achannel 18 disposed in a sprue bushing 20 heated by electricalresistance heating element 22 and is distributed through manifoldchannels 24 defined in heated (or heatable) manifold 26. The heatedmanifold is provided with electrical resistance heating elements 28capable of maintaining the resin at a desired temperature thatfacilitates flow. The resin flows from the manifold channels 24 into anannular space 30 defined between internal walls 32 of nozzles 34 and avalve pin 36 that is linearly movable within nozzle 34 along a verticallongitudinal axis of the nozzle between an open position (shown for thenozzle on the left in FIG. 1) and a closed position (shown for thenozzle on the right in FIG. 1). When the valve pin 36 is in the openposition, liquid resin flows into mold cavity 12. Nozzles 34 aremaintained at a temperature sufficient to keep the resin in a liquid(flowable) state by electrical resistance heating elements 38. Nozzles34 can be provided with external threads 40 on the inlet end of thenozzle which engage internal threads of a bore through the bottom ofmanifold 26 to provide a fluid-tight seal. The mold can define a singlecavity or multiple cavities, and each cavity can be supplied with resinfrom a single nozzle or multiple nozzles.

The position and rate of movement of valve pins 36 are controlled by anactuator 100. Actuator 100 includes a body and/or housing for anelectric motor 101 and converts rotational movement of the electricmotor into linear movement (up and down in FIG. 2) of a drive shaft 102,which in the illustrated example has an elongate internally threadedbore 104. Rotation of motor 101 generally around axis 105 can beconnected to linear movement of drive shaft 102 such as by providingthreaded structure on the rotor of electric motor 101 that engagesexternal threads on drive shaft 102. The extent of travel of drive shaft102 can be limited to the confines of the body of actuator 100. Bore 104has a central axis 105 coincident with the central axis of pin 36 andnozzle 34. The body and/or housing of actuator 100 has a bottom opening107 and a top opening 109 that allows access to threaded bore 104 toallow an externally threaded valve pin nut 106 to be threaded into bore104. A lock nut 108 can be threaded into bore 104 from the top openingto lock the position of nut 106 and valve pin 36 after it has beenadjusted. A lower end of nut 106 has an inwardly projectingsemi-circumferential rim 111 that engages a circumferential groove 112at an upper end of valve pin 36 to secure valve pin 36 to nut 106. Anopening in the rim allows the valve pin 36 to be inserted into nut 106.The threaded connection between valve pin nut 106 and drive shaft 102can be replaced with a fixed or other connection between the shaft 102and nut 106, although this would eliminate the possibility of manuallyadjusting the valve pin position (as described below).

Nut 106 has a tool-head engagement structure 114 that can be engaged bya tool, such as an allen wrench to allow manual adjustment of theposition of nut 106 and pin 36. Similarly, lock nut 108 has a tool-headengagement structure 116 to allow tightening of lock nut 108 againstvalve pin nut 106 using a tool such as an allen wrench. In theillustrated embodiment, engagement structures 114 and 116 are hexagonalsockets. However, other shapes or tool-engagement means are possible.Top plate 64 can be provided with openings or bores 117 to allow accessto tool engagement structure (e.g., sockets 114, 116) to allow manualadjustment of the valve pin position without removal of plate 64 ordisassembly of hot-runner assembly 10.

Electrical connectors 118, 120 are provided for powering and controllingthe electric motor, and to power and receive signals from an encoderthat tracks drive shaft position.

A coolant inlet port 122 and a coolant outlet port 124 are provided toallow a coolant (e.g., chilled water or oil) to be circulated throughthe body and/or housing of the actuator to protect the motor againstdegradation or failure caused by overheating.

Actuator 100 can be supported on an insulating support member 126.Support 126 can, and preferably does, have a relatively low thermalconductivity. Preferred materials for member 126 are stainless steel andtitanium or other material having a thermal conductivity equal to orless than the thermal conductivity of titanium. Support 126 can bereleasably secured to manifold 26, such as with screws or bolts (notshown).

When assembled, the upper end of valve pin 36 extends into bore 104through openings in manifold 26, support 126 and the body or housing ofactuator 100 to provide a vertically compact design for apparatus 10.

An anti-rotation plate or guide 130 can be releasably secured to support126 with bolts 132. Plate 130 has an aperture 134 for passage of valvepin 36. Aperture 134 has a shape configured to engage a section of valvepin 36 having a non-circular profile to prevent rotation of the pinaround the longitudinal axis of the pin 36 and nozzle 34. In theillustrated embodiment, the non-circular profile includes two opposingflat or planar surfaces 136 (one of which is shown in FIG. 3). Whileflat surfaces 136 are engaged by straight edges of aperture 134 in theillustrated embodiment, other anti-rotational means can be provided,such as splines, grooves, and other structures that can prevent rotationof valve pin 36.

Manifold 26 and actuators 100 are located in a space generally boundedby a top mold plate 64 and an intermediate mold plate 66.

Assembly 10 can also include various lower support elements 68, dowels70, and upper support elements 72 for facilitating proper alignment andspacing of the components of the assembly.

A pin seal 138 prevents liquid resin from leaking upwardly from channel24 of manifold 26.

The disclosed apparatus allows adjustment of the valve pin usingdedicated tools/wrenches etc. from the back side of the actuator(opposite valve pin or valve pin elongation side).

The disclosed apparatus can allow coupling and decoupling of the cooledactuator axially to the valve pin.

The valve pin can be suspended within the height of the actuator.

The disclosed apparatus can also allow mounting of the cooled actuatoraxially to the valve pin on a thermal insulation support in directcontact to the hot-runner manifold; wherein the support can protrudealong the actuator corners.

Shown in FIG. 4 is an alternative arrangement in which the valve pin 36is indirectly coupled to drive shaft 102 (rather than directly as shownin FIGS. 1 and 2) by a valve pin extension 140.

The actuator 100 can be installed and coupled to the valve pin 36axially, i.e., without moving the actuator laterally away from axis 105.This can be accomplished by first positioning the valve pin through themanifold and into the associated nozzle with an upper end of the valvepin projecting upwardly from the top of the manifold (i.e., the surfaceopposite the surface from which the nozzles extend). Thereafter, support126 can be attached to the manifold (such as with screws) andanti-rotation plate 130 can be positioned around valve pin 36 andsecured to the support with bolts 132. Next, nut 106 can be positionedonto the head (top end) of valve pin 36. Actuator 100 is then positionedwith the bore of drive shaft 110 in axial alignment with the valve pin.The tool engagement structure of nut 106 can then be accessed via thetop opening 109 of actuator 100 with a tool to rotate nut 106 and threadnut 108 into the threaded bore 104 of driveshaft 102.

The above description is intended to be illustrative, not restrictive.The scope of the invention should be determined with reference to theappended claims along with the full scope of equivalents. It isanticipated and intended that future developments will occur in the art,and that the disclosed devices, kits and methods will be incorporatedinto such future embodiments. Thus, the invention is capable ofmodification and variation and is limited only by the following claims.

What is claimed is:
 1. An injection molding apparatus, comprising; amanifold defining a resin channel for conveying liquid resin from aninjection molding machine toward a mold cavity; a nozzle for conveyingliquid resin from the resin channel to the mold cavity; a valve pinconfigured for linear movement along a longitudinal axis of the nozzleto control flow of liquid resin through the nozzle; an electric actuatorhaving a body containing an electric motor and a liner drive shaft witha bore, wherein both the electric motor and the linear drive shaft arecontained within the body of the electric actuator, and wherein thevalve pin is directly or indirectly coupled to the drive shaft withinthe bore, such that linear movement of the drive shaft producesco-linear movement of the valve pin; wherein the bore extending throughthe drive shaft is internally threaded and the valve pin is directly orindirectly coupled to the drive shaft via an externally threaded valvepin nut threadingly engaging the internally threaded bore; wherein thevalve pin nut has a tool-head engagement structure for manualpositioning of the valve pin and valve pin nut with respect to the driveshaft; and further comprising an externally threaded lock nutthreadingly engaging the internally threaded bore and disposed adjacenta side of the valve pin nut opposite the valve pin.
 2. The apparatus ofclaim 1, wherein the lock nut has a tool-head engagement structure formanual tightening of the lock nut against the valve pin nut.
 3. Aninjection molding apparatus, comprising: a manifold defining a resinchannel for conveying liquid resin from an injection molding machinetoward a mold cavity; a nozzle for conveying liquid resin from the resinchannel to the mold cavity; a valve pin configured for linear movementalong a longitudinal axis of the nozzle to control flow of liquid resinthrough the nozzle; and an electric actuator having a body containing anelectric motor and a linear drive shaft with a bore, wherein both theelectric motor and the linear drive shaft are contained within the bodyof the electric actuator, and wherein the valve pin is directly orindirectly coupled to the drive shaft within the bore, such that linearmovement of the drive shaft produces co-linear movement of the valvepin; and wherein the electric actuator is mounted on a support attachedto the manifold, and further comprises an anti-rotation plate disposedbetween a bottom of the support and the electric actuator and releasablyattached to the bottom of the support, the anti-rotation plate having anaperture for passage of the valve pin, the aperture having a shapeconfigured to engage a section of the valve pin having a non-circularprofile to prevent rotation of the pin around the longitudinal axis ofthe nozzle.